Rockwell Automation Logix5000 Controllers Add-on Instructions Programming Manual - Manual (Page 22)

Chapter 1 Designing Add-On Instructions
The Instruction Help Preview shows how your instruction will appear in the
various languages, based on parameters defined as required or visible.
When deciding whether to develop an Add-On Instruction, consider the
following aspects.
Instruction functionality
Complex instructions tend to be highly application specific and not reusable, or
require extensive configuration support code. As with the built-in instructions,
Add-On Instructions need to do one thing, do it well, and support modular
coding. Consider how the instruction will be used and manage interface
complexity for the end user or application.
Add-On Instructions are best at providing a specific type of functionality or device
control.
Encapsulation
Add-On Instructions are designed to fully encapsulate the code and data
associated with the instruction. The logic inside an Add-On Instruction uses only
the parameters and local tags defined by the instruction definition. There is no
Considerations for Add-On
Instructions
22 Rockwell Automation Publication 1756-PM010F-EN-P - October 2014